An annular gas turbine engine combustion chamber comprises an annular upstream end wall, an inner annular wall and an outer annular wall. The annular upstream end wall has a plurality of circumferentially spaced apertures and an associated fuel injector is located in each of the apertures in the annular upstream end wall.
Conventionally an annular gas turbine engine combustion chamber is provided with a plurality of heat shields, tiles, arranged downstream of the annular upstream end wall to thermally protect the upstream wall of the combustion chamber. Each heat shield, tile, is provided with a central aperture which is aligned with a corresponding aperture in the annular upstream end wall and the associated fuel injector.
The annular gas turbine engine combustion chamber is provided with a plurality of tiles arranged radially outside of the inner annular wall to thermally protect the inner annular wall of the combustion chamber and a plurality of tiles arranged radially inside the outer annular wall to thermally protect the outer annular wall of the combustion chamber.
Conventionally each heat shield is provided with a plurality of pedestals, or projections, which extend in an upstream direction away from the upstream, cold, surface of the heat shield. Similarly, each tile on the inner annular wall is provided with a plurality of pedestals which extend in a radially inwardly direction from the radially inner, cold, surface of the tile and each tile on the outer annular wall is provided with a plurality of pedestals which extend in a radially outwardly direction from the radially outer, cold, surface of the tile. The pedestals provide cooling of the heat shield and/or tile by conducting heat away from the heat shield and/or tile and the heat is transferred to coolant flowing around and between the pedestals. These pedestals are arranged in regular patterns on the heat shields and tiles, for example the pedestals are arranged in a hexagonal pattern with a pedestal arranged at each of the six corners of the hexagon and a pedestal arranged at the centre of the hexagon and thus the pedestals are arranged in a plurality of parallel straight lines. The pedestals are generally circular in cross-section.
However, it has been found that the tiles suffer from cracking during service in a gas turbine engine combustion chamber and in some circumstances a tile has failed due to a crack extending all the way across the tile. A crack generally forms along a weak line, or weak section, of a tile, e.g. a line or section of the tile which is weaker than the remainder of the tile, and it has now been found that the regular, hexagonal, pattern of pedestals on a tile produces one or more weak lines or weak sections. The crack generally forms substantially in a line between two adjacent rows of pedestals. The weak lines, or weak sections, have lower bending stiffness than the remainder of the tile and are susceptible to failure with various resonant frequencies and with thermal and pressure loading in the combustion chamber.
Alternatively, each tile on the inner annular wall is provided with a plurality of effusion cooling apertures which extend through the tile to provide a film of coolant on the radially outer, hot, surface of the tile and each tile on the outer annular wall is provided with a plurality of effusion cooling apertures which extend through the tile to provide a film of coolant on the radially inner, hot, surface of the tile. These effusion cooling apertures are arranged in regular patterns on the tiles, for example the effusion cooling apertures are arranged in a hexagonal pattern with an effusion cooling aperture arranged at each of the six corners of the hexagon and an effusion cooling aperture arranged at the centre of the hexagon and thus the effusion cooling apertures are arranged in a plurality of parallel straight lines. The effusion cooling apertures are generally circular in cross-section.
However, there is a possibility that these tiles may suffer from cracking during service in a gas turbine engine combustion chamber and in some circumstances it may be possible that a tile may fail due to a crack extending all the way across the tile. A crack generally forms along a weak line, or weak section, of a tile, e.g. a line or section of the tile which is weaker than the remainder of the tile. It is postulated that the regular, hexagonal, pattern of effusion cooling apertures on a tile may produce one or more weak lines or weak sections in a similar manner to the tiles with pedestals. The crack generally forms substantially in a line of effusion cooling apertures. The weak lines, or weak sections, have lower bending stiffness than the remainder of the tile and may be susceptible to failure with various resonant frequencies and with thermal and pressure loading in the combustion chamber.
It is therefore necessary to periodically inspect a combustion chamber using a boroscope to determine whether a tile has cracked, or has not cracked, and if it is determined that a tile has cracked it is replaced.
Therefore the present disclosure seeks to provide a novel annular combustion chamber wall and tile arrangement which reduces or overcomes the above mentioned problem.